1. Field of the Invention
The present invention relates to a tool for use in realigning the wheels of an automotive vehicle, especially four wheel drive vehicles, and a method of realigning the wheels of such vehicles.
2. Description of the Prior Art
With continued or heavy duty use, the wheels of automotive vehicles sometimes become misaligned. Misalignment can occur as a result of wear or bending of the wheel support structures. Axles and spindles sometimes become bent when a vehicle is driven over rough roads or terrain. The ball joints which support the spindle mounting can also wear or become bent. When wheels of a vehicle become misaligned, the vehicle can become difficult to steer and operation of the vehicle can become unsafe. In any event, misalignment inevitably results in excessively rapid and uneven wear on the vehicle tires.
A typical wheel mounting includes a wheel mounted on a spindle which projects outwardly from a generally vertically oriented mounting bracket. In conventional passenger vehicles the mounting bracket, mounting plate and spindle are all formed as a unitary structure. In four wheel drive (4WD) vehicles, on the other hand, the spindle and mounting plate are formed as a unitary structure and are bolted to a mounting bracket. The mounting bracket is equipped with a pair of inwardly directed arms which are hingedly coupled to corresponding mounting arms on another mounting bracket which is stationary relative to the vehicle frame. The stationary and hinged mounting brackets are connected together by a pair of ball joint connections which are nearly vertically aligned. The angular departure of the ball joint connections from perfect vertical alignment in a fore and aft direction relative to the vehicle chassis is called caster. The manufacturer's specification for caster may vary as between different vehicle models, but the prescribed caster is usually within five degrees of perfect vertical alignment.
According to convention, caster of a vehicle wheel is negative if the upper ball joint of a vehicle wheel is forward of the lower ball joint, and positive if the upper ball joint is aft of the lower ball joint.
The other major parameter in which vehicle wheel alignment is measured is termed camber. Camber is the term used to describe the upright orientation of a vehicle wheel measured transversely relative to the vehicle chassis. The camber of a wheel is measured in degrees and is zero degress if the wheel resides in a vertical plane. Camber is negative if the top of the wheel is located inwardly toward the vehicle frame relative to the bottom of the wheel and positive if the top of the vehicle wheel is located outwardly from the bottom of the vehicle wheel relative to the vehicle frame.
Manufacturers specify proper wheel alignment for each model of vehicle manufactured in terms of caster and camber. When misalignment occurs, corrections are performed by first measuring the extent to which the caster and camber of the vehicle wheels depart from the manufacturer's specifications. Steps are then taken to eliminate any caster and camber deviations from specification.
In conventional practice, vehicle wheel realignment is initiated by parking the vehicle so that the wheels rest atop the turntables of a wheel alignment rack. The wheel hubcap and spindle cap are first removed and a conventional camber-caster gauge is positioned against the exposed end of the wheel spindle so that it bears against the wheel hub, the brake drum or rotor assembly.
A conventional camber-caster gauge includes a fitting which is designed to fit in abutting fashion against the exposed end of the rotor, and a pair of parallel degree gauges one for measuring caster and one for measuring camber, both of which extend parallel to the spindle. The two parallel degree gauges are typically bubble gauges. The inclination of the caster gauge relative to a horizontal orientation can be adjusted.
The measurement of camber is performed with the wheel in exact fore and aft alignment, as measured by radial gradations on the base of the alignment rack beneath the turntable. The camber bubble gauge will thereupon be oriented in a generally horizontal disposition in a direction perpendicular to the alignment of the vehicle frame. If the bubble in the bubble gauge rises toward the outboard side of the zero inclination mark of the gauge, a negative camber is indicated. Conversely, if the bubble in the gauge rises toward the inboard end of the gauge, a positive camber is indicated.
The caster bubble gauge is parallel to the camber bubble gauge. Caster is measured by first rotating the wheel on the turntable of the alignment rack so that the spindle is brought 20 degrees to the rear of alignment perpendicular to the orientation of the vehicle frame. The level of the caster bubble gauge is adjusted so that the bubble is precisely at the zero mark on the gauge. The wheel is then turned on the turntable to bring the spindle precisely 20 degrees forward of perpendicular alignment relative to the alignment of the vehicle frame. The extent to which the bubble in the caster gauge departs from the zero mark on the gauge is indicative of the caster measurement for that wheel. That is, a rise of the bubble toward the outboard end of the caster gauge will indicate a positive caster, while a migration of the bubble toward the inboard end of the gauge will indicate a negative caster.
Measurements of caster can only be performed with a sophisticated electronic alignment mechanism, or with a conventional camber-caster gauge attached to the hub, rotor or drum, with the vehicle wheel mounted on the spindle, and with the vehicle resting on a wheel alignment rack. Wheel alignment racks are rather expensive, and most automotive repair establishments capable of performing wheel alignments have a minimum number of wheel alignment racks because of the expense involved. This reduces the rate at which wheel alignments can be performed, since a vehicle remains on the wheel alignment rack, once camber and caster have been measured, for the entire alignment process.
Corrections in wheel alignment are, on four wheel drive vehicles, typically performed by installing eccentrics in the upper ball joint carrying the spindle mounting plate, by installing shims between the spindle base and the spindle mounting plate, or by using a combination of both of these correction techniques. An eccentric is an externally threaded fitting which replaces the original annular, externally threaded fitting in the upper ball joint. Unlike the original fitting, an eccentric has a longitudinal bore which departs slightly from axial alignment. The degree of departure controls the amount of correction of caster and camber which will be achieved.
The eccentric is tightened down in place of the original fitting until a minimum preloading of the ball joint is achieved. Thereafter, continued threadable engagement of the eccentric into the upper ball joint arm will control the alignment of the upper ball joint relative to the lower ball joint both in a direction transverse to the vehicle frame, and in a direction parallel to the orientation of the vehicle frame. In this manner, corrections for both camber and caster can be achieved.
However, according to conventional wheel realignment techniques, it is impossible to continuously monitor both camber and caster while installing an eccentric. This is because caster can only be measured with the wheel on the spindle and with the vehicle on the wheel alignment rack.
Another technique for realigning vehicle wheels involves the installation of a shim. A shim can only be used on those vehicles in which the spindle and spindle base are on a structure separate from the spindle mounting bracket. An annular shim is inserted between the mounting bracket and the spindle base. The annular shim has a wedge shaped cross-section, so as to alter the orientation of the spindle relative to the horizontal. A shim is used only to effectuate corrections for camber by reorienting the spindle alignment relative to the horizontal. Any fore and aft alignment is meaningless because the spindle is constantly moved fore and aft by the vehicle steering wheel when the vehicle is in operation. Nevertheless, a shim can be used in conjunction with an eccentric to provide greater flexibility in adjustments to both camber and caster.
In conventional automotive vehicle wheel alignment, camber and caster are first checked with the vehicle on the wheel alignment rack. The wheels are then removed from the vehicle spindles. The appropriate corrective measures are then taken to attempt to bring the camber and caster back to the manufacturer's specification. That is, an eccentric is installed, a shim is installed, or both an eccentric and a shim are installed on the vehicle wheel mounting. While camber can be monitored during the remedial techniques, caster cannot. Caster can only be checked again once the corrective measures have been completed, the wheels reinstalled on the vehicle, and with the vehicle resting on the wheel alignment rack. If caster has not been corrected sufficiently, the vehicle must again be raised and further corrective measures must be taken. This trial and error process in effectuating wheel realignment results in considerable expense due to the labor charges involved.